A vehicle “consist” is group of two or more vehicles mechanically coupled or linked together to travel along a route. For example, a rail vehicle consist is a group of two or more rail vehicles that are mechanically coupled or linked together to travel along a route, as defined by a set of rails that support and guide the rail vehicle consist. One type of rail vehicle consist is a train, which may include one or more locomotives (or other powered rail cars/vehicles) and one or more non-powered rail cars/vehicles. (In the context of a rail vehicle consist, “powered” means capable of self propulsion and “non-powered” means incapable of self propulsion.) Each locomotive includes traction equipment for moving the train, whereas each rail car is configured for hauling passengers or freight. For producing motive effort, most modern locomotives use electric motors. In a typical case, a locomotive will include plural motors. For each motor, a pinion gear is attached to the output shaft of the motor, for driving a bull gear operably attached to a traction wheel set of the locomotive. For operation of the motor, the motor is supplied with electricity. In some locomotives, the locomotive may include an on-board power source for providing traction electricity (meaning electricity of suitable magnitude to power traction motors for moving a train). In other locomotives, traction electricity is received from an off-board source, such as a third rail or an overhead catenary line.
Rail vehicles typically include an airbrake system. The airbrake system includes a source of pressurized air, and, on each rail vehicle, a brake pipe, a brake mechanism, and one or more valves or other control elements for controlling braking. When rail vehicles are assembled in a consist, the brake pipe interconnects the vehicles of the consist. The brake mechanism on each vehicle is reverse pressure dependent, meaning the mechanism is deactivated (no braking) when pressure is present, and activated when pressure is not present. This facilitates automatic emergency braking if air pressure is lost.
During operation of a rail vehicle consist, if a component of the airbrake system fails, the consist may be brought into an emergency or other contingent operational mode. For example, information of a failure may be detected remotely and communicated to a lead locomotive or other rail vehicle, with the operator bringing the consist to a stop. Alternatively, in some systems and depending on the failure in question, the consist may be automatically controlled to a stop. In either case, the crew must walk back along the train in an attempt to correct the failure, and/or call in additional locomotive assets, such as a helper locomotive to assist in charging the brake pipe or removing vehicles/cars from the consist. Thus, not only is the consist itself delayed, but the track on which it is traveling is blocked. Additionally, depending on weather conditions and the current location of the consist, it may be dangerous for the crew to walk back to a remote part of the consist for attempting to correct the failure.